Molecular cloning, characterization and isolation of novel spliced variants of the human ortholog of a rat estrogen-regulated membrane-associated protein, UO-44

We have previously reported the characterization of an estrogen-regulated rat uterine-ovarian-specific complementary DNA (UO-44). To understand the involvement of this protein in the initiation and progression of human ovarian and uterine cancers, we now report the cloning and characterization of the human ortholog (HuUO-44). HuUO-44 is mapped to chromosome 10q26.13 and contains nine exons. Multiple tissue Northern blot detected two HuUO-44 transcripts of approximately 2 and 3 kb in the pancreas. RT-PCR demonstrated that HuUO-44 undergoes a complex series of alternative splicing events between exons 2 and 6 that yielded four novel splice variants, HuUO-44A, HuUO-44B, HuUO-44C and HuUO-44D. Putative functional motifs identified in HuUO-44 are two CUB domains and a zona-pellucida domain. Transfection studies demonstrated the membrane-associated nature of HuUO-44. By immunohistochemistry, HuUO-44 was located to the normal ovarian and ovarian tumor epithelial cells; in NIH-OVCAR3 ovarian Cancer cells, HuUO-44 was detected only at the leading edge of the dividing cells. Most importantly, a marked loss in cell attachment and proliferation was observed in NIH-OVCAR3 cells cultured in the presence of a polyclonal HuUO-44 antiserum. These findings suggest the potential role of HuUO-44 in cell motility, cell-cell interactions and/or interactions with the extracellular matrices.